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3
OPEN VENTED SYSTEM REQUIREMENTS
Detail reference should be made to the appropriate
standards listed on page 4.
The information and guidance given below is not
intended to override any requirements of the above
publications or the requirements of the local authority,
gas or water undertakings.
The vertical distance between the pump and feed/
expansion cistern MUST comply with the pump
manufacturer's minimum requirements, to avoid
cavitation. Should these conditions not apply either
lower the pump position or raise the cistern above the
minimum requirement specified by Caradon Ideal
Limited. The isolation valves should be fitted as close
to the pump as possible.
The boiler is fitted with an automatic air vent. This air
vent must never be shut off, as this could result in dry
firing of the boiler and subsequent damage to the heat
exchanger.
The information provided is based on the following
assumptions:
1. An independent open vent/safety pipe connection is
made immediately after the system flow pipe
connection.
2. An independent cold feed/expansion pipe
connection is made immediately after the open
vent/safety pipe connection.
3. The maximum flow rate through the boiler is based
on a temperature difference of 11ºC at full boiler
output.
4. The boiler is at the highest point of circulation in the
system. Systems designed to rise above the boiler
flow tappings will automatically require a minimum
static head higher than that shown.
5. The position of the open vent/safety pipe above the
expansion cistern water level is given as a guide
only. The final position will depend upon the
particular characteristics of the system. Pumping
over of water into the expansion cistern must be
avoided.
6. Both open vent/safety pipe and cold feed/expansion
pipes must be of adequate diameter to suit the
output of the boiler. Refer to Tables 4 and 5.
Table 4 Open Vent Pipe Sizes
Rated output
Minimum bore
kW
61 to 150
151 to 300
'Steel pipe sizes complying with medium or heavy quality or
BS 1387.
-
Installation & Servicing
GENERAL
Nominal Size (DN)'
mm
32
32
38
40
Feed/expansion
cistern
Water
level
(cold)
Open vent
Connections
to boiler
Note.
•
With a cold feed head of <8m, the pump must
be fitted on the return to the boiler.
•
This diagram does not show safety valves,
water flow switches, etc. necessary for the safe
operation of the system.
Table 5 Cold Feed Pipe Sizes
Rated output
Minimum bore
kW
61 to 150
151 to 300
'Steel pipe sizes complying with medium or heavy quality or
BS 1387.
Note.
Refer to Frames 23 and 24 for typical system arrangements.
Open vent
safety pipe
3 m
Cold
minimum
Feed
see notes
System
flow
Inverted cold
feed entry
System
return
Nominal Size (DN)
mm
in'
25
1
1
32
1
/
4
9
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